The common name of the Anegada Island Iguana is misleading, as the animal was once distributed over the entire Puerto Rico Bank. Fossils are known from Saint Thomas and Puerto Rico. Vulnerability to predation by humans and their dogs and cats may have resulted in a contraction of its distribution to Anegada.

Population density in 1968 was estimated at 2.03/ha (Carey 1975). In 1991, this figure had dropped to 0.36/ha in comparable habitat. Extrapolation of density estimates, distribution, and relative habitat quality yields a population estimate for Anegada of 164 individuals. A small restored population also exists on Guana Island with eight founding adults (Goodyear and Lazell 1994), from which three juveniles have been translocated to Necker Island. The total population, including individuals on Anegada, Guana, and Necker probably consists of fewer than 200 individuals.

Estimates in the late 1960s (Carey 1975) showed small home ranges for both sexes (less than 0.1 ha), one principal burrow per animal, a 1:1 sex ratio, and habits that indicated monogamy (apparent pairs inhabited separate but proximate burrows in a joint home range isolated from other pairs). The current population structure is quite different. While previous studies may not have been sensitive to long range movements, it now appears that home ranges are quite large on Anegada: males average 6.6 ha and females average 4.2 ha. Home ranges broadly overlap and have one or two centers of activity. In 1991 the sex ratio had dropped to 1 female:2 males. Thus male competition for limited females may be responsible for the high degree of home range overlap.

Burrows of both sexes may be located on the old limestone reef-tract or in sandy areas adjacent to it. If available, iguanas will use additional holes or crevices as emergency retreats. Whereas degraded vegetation may provide for male subsistence, it may not provide females with sufficient energy to allow them both to produce eggs and compete with other animals for forage to support their own growth and metabolism. Reproducing females may have low survivorship, resulting in the present skewed sex ratio. Females usually lay one clutch of about 12-16 eggs per year in late spring or early summer.

Although largely facultative herbivores, all age-groups of these iguanas are opportunistic carnivores. Invertebrates (beetles, caterpillars, centipedes, roaches) form less than 1% of the natural diet, although this may be a result of limited availability. The bulk of the diet consists of leaves and fruits.

Over the past 20 years, grazing pressure by goats, sheep, burros, and cattle has radically changed the vegetation composition of Anegada. The iguanas' diet is now composed of plant species the feral animals reject.

Areas on Anegada that once contained dense populations of iguanas now support few or none. Research indicates that this is due to three major causes, including competitive grazing pressure from free-ranging livestock, predation by feral dogs, and predation of juveniles by feral cats.

A major grant has been received from the Environment, Science and Energy Department of the UK Foreign Commonwealth Office to facilitate conservation activities on Anegada. Goals of this program are to 1) implement a cat eradication/control feasibility study, 2) expand the current headstart facility, 3) train the Senior Terrestrial Warden in iguana husbandry and facility maintenance, 4) conduct population censusing and mapping at sites nesting sites and other potential sites where adults may be found, and 5) develop environmental education materials to raise public awareness of the importance and vulnerability of iguanas on Anegada.

In the 1980s, eight iguanas were moved from Anegada to Guana Island, British Virgin Islands, to start a second population in part of the species’ former range (Goodyear and Lazell 1994). This is not a limestone island, and does not provide as many natural retreats as Anegada. In the absence of introduced predators, however, the iguanas appear to do well and reproduce in areas that are free of sheep (the only feral grazing competitor present). Currently, approximately 20 adult iguanas are estimated to inhabit Guana. Offspring have been seen each year since 1987, but recruitment is very low over much of the island. Guana Island Wildlife Sanctuary continues to try to rid the island of sheep, which may improve the habitat for iguanas.